Chromatography, theory Peak width as a function of retention time and capacity ratio "abt" concept Real plate height and theoretical plate height Extra-column contributions to band broadening and "abt" concept
Summary
Kaiser's "abt" concept rests on the experimental establishment of a linear relation between band width at half height, b0.5, and capacity ratio, k, according to b0.5 = b, + ak His column specification quantity, h , a l , is dependent on the square of the slope a, obtained from a linear regression analysis based on this relation. It is shown in the present paper that an improvement of the experimental conditions leading to a lower extra-column contribution to band broadening, bix, introduces a tendency towards a negative curvature in the plot at low k values. The mean slope increases, and an uncritical linear regression would yield an h,,l -val ue which is higher than before and which would be in the opposite direction to the requirements of a reliable column specification. Generally the linear regression analysis has to be moved to higher k regions in cases of curvature, especially as it is also shown that h , , l is an estimation of the traditional HETP value, H , , that would be obtained when k approaches infinity. This theoretically expected relation hreal = His a strong motivation for the use of hreal as a column specification, since the bo,s-value associated with H, is expected to be practically independent of b%.